Electronic timer



June 1948- w. E. LARGE ETAL ELECTRONIC TIMER Filed May 19, 1945INVENTORS W//// am E Z ary and WIUF E Monk/2.

WITNESSES: TZ

ATTORN Y Patented June 22, 1948 UNITED JSTiATE-E'a PATENT OFFICEELECTRGNIC Tilt ERR William E. Large, Pittsburghgla.,and Wilbur It.

Morton, Qal: Ridge, Tenn, assignors to Westinghouse Electric(.lorneration, East Pittsburgh, Pa, corporation of Pennsylvania 1945,Serial No. 594,766

Application 19,

Claims.

This invention: relates to a timing system and has particular relationtoan electronic timing system for use withwelding apparatus;

In resistance spot weldinggood quality welds ma be obtained .hy=a methodknown aspulse.- tion welding. A typical control.system for pulsationwelding-is shown in. the Pearson and Stadum-Patent No. 2,340,077, issuedJanuary 25, 194:4, and assigned to the .Westinghouse Electric taMaiutacturing Company. In I this system, discrete impulses'of currentare supplied to the materials to-be welded through a pair ofinverselyconnected electric discharge valves of the arc-lilac type, such asignitrons, from' an alternating voltage source. Each of the currentimpulses is of a predetermined length, and there is a predeterminedtimeinterval between. successive impu ses. Since the end of a Weldingvcurrent impulso coincides with the end ota half-period of thealternating voltage because of the well-known characteristicsofthe'ignitrons, it is necessary to initiate a welding current impulsein synchronism with the alternating voltage to maintainthe product ofwelding current and time substantially constant to produce uniform weldsof good quality.

While the apparatus described in the Pearson and Stadulm patent operatessatisfactorily, it is highly desirableirom the standpoint of both theinitial coat and the cost of maintenance to re du'cc the number ofelementsinthe system and simplify the construction and operation. It is,accordingly, an'object of our invention to provide a new and improvedpulsation timing system.

Another object ofour invention is to provide a novel timing systemfor apulsation welding control which has a simplified construction andoperation.

A further object of our invention is to provide a new'and improvedsystem-for supplying power from a periodically pulsating source to aload in discrete impulses, 'each'imnulsebeing ofa predetermined lengthwith a predetermined timeinterval' between 'successive'impulses.

More specifically, it is an'obiect of our invention to providc a new andimnroved soot welding pulsation control system for synchronous opera--tion: from an alternating-current source, which system employs aminimumnumber of electrical elements.

In accordance with our inventiomwe provide timing apparatus whichincludes a first timing system, hereinafter referred to as the on-timetiming system, for measuring the interval of current flow. A secondtiming system, refer ed to hereinafter as an off i he timing system,provided {or measuring the interval'between successive impulsesofwelding current. The oil-time, timing system is quite similar to thatdisclosed in the aforesaid Pearson and Stadum patent, but a new and.greatly simplified off'timet-iming system is employed.

The novel features that we consider character istic of our invention areset forth with particularity in the appended claims. The inventionitself, however, both as-to its organizationv and its method ofoperation, together with additional objects and advantages thereof, maybest be understood from the following description a specific embodimentwhen read in connection with the accompanying drawing, the single figureof which is a schematic circuitdiagram of pre- .ferred embodiment of ourinvention.

As illustrated in the drawing, current is supplied from a source ofalternating current 2 through supply lines 3 and 4 and a pair of ig--nitrous 5 and I connected in amt-parallel, to the primary 9 of thewelding transformer II. The secondary l3 of the Welding transformer isconnected across the electrodes [5 and H in engage" ment with thematerial 19- to be welded.

Each of the ignitrons 5 and 1 includes an anode 2!, a mercury noolcathode 2-3. and an igniter 25 in contact with the cathode. The ignitioncircuit for one of the ignitrons 5 maybe traced from V supply line 3through the primary 9 of the transformer H, the anode 2i and cathode 29of an electric discharge valve and the igniter 2.5 and cathode 230i theignitron 5 to theother supply line 4. The ignition circuit of the otherignitron 1 may be traced from suppl line through the anode 33 andcathode 35 of another electric discharge valve 3'l, the igniter 25 andcathode 23 of the ignitron l and primary ll to the supply line 3. Theelectric discharge valves Bl and 37 in the ignition circuits of theignitrons 5 and 'l are of the arc-like type, such as thyratrons, and arehereinafter referred to as the-firing tubes;

The firing tube 3i for the first ignitron 5 is controlled :by an on-timetiming system 39. The control circuit of the firing tube 3'! for thesec- 3 ond ignitron 1 may be traced from the grid 45 through a gridresistor 4|, the secondary 43 of an auxiliary transformer 45, a biasingpotential source 41, to the cathode 35. The primary 49 of the auxiliarytransformer 45 is connected directly across the primary 9 of the weldingtransformer.

The arrangement described for control of the firing tube 31 for thesecond ignitron 1 is known as a follow-up system. The first ignitron 5is rendered conductive initially and when it ceases to conduct, thereactance of the welding transformer primary 9 acts through theauxiliary transformer to cause a potential impulse in the controlcircuit of the firing tube 31 to render the firing tube conductive. As aresult, the second ignitron 1 is rendered conductive.

The on-time timing system 39 is energized from the supply lines 3 and 4by means of an auxiliary transformer 51 and a rectifying system 53 whichimpresses a direct-current potential across a voltage divider 55. Anelectric discharge valve 51 of the arc-like type, such as a thyratronwhich is hereinafter referred to as a start valve, has its anode 59arranged to be connected to the positive terminal 33 of the voltagedivider 55 upon closure of normally open contacts 69 of a relay TI. Thecathode SI of the start valve is connected to an intermediate tap nearthe negative end of the divider 55 through a resistor 61.

The control circuit of the start valve 51 may be traced from the grid 13through a grid resistor 15, a second resistor 11, the lower portion 19of the voltage divider 55, a conductor BI and resistor I51 to thecathode 6| The potential across the lower portion 19 of the dividertends to maintain the start valve 51 non-conductive after the contacts59 of the relay H are closed. However, a potential impulse is impressedacross the resistor 11 in the control circuit from the supply linesthrough a phase-shifting circuit 82 and an impulsing transformer 83.This potential impulse counteracts the biasing potential of the lowerportion 19 of the divider to render the start valve conductive Thephase-shifting circuit 82 is preferably so adjusted with respect to thepower factor that the start valve 51 becomes conductive at the beginningof a half period of the alternating current in which the anode 21 of thefiring tube 31 is positive.

An electric discharge valve 84 of the arc-like type, such as a thyratronwhich is hereinafter referred to as :a stop valve, has its anode 86arranged to be connected to the positive terminal 63 of the voltagedivider 55 upon closure of the contacts 69. The cathode 95 of the stopvalve is connected to the intermediate tap of the divider through theenergizing coil of a relay 92.

The control circuit of the stop valve 84 extends from the grid 81through a grid resistor 39, a conductor 9|, a capacitor 93, to the lowerintermediate tap 65 of the divider. The control circuit'continues fromthe intermediate tap 85 through coil 90 to the cathode 0f the stopvalve. The capacitor 93 is also connected in series with the start valve51 through a rectifier 91 and 'a timing potentiometer 9. A dischargecircuit is provided across the capacitor 93 through an originally closedcontact 94 of relay 1I. This contact 94 is opened when contacts 69 areclosed.

When the start valve 51 becomes conductive,

the capacitor 93 is charged at a rate which is determined by the settingof the potentiometer '99. The portion of the voltage divider in thecontrol circuit of the stop valve 84 tends to maintain itnon-conductive, but after a predetermined interval of time, thecapacitor 93 is charged to a suflicient potential to counteract thebiasing potential of the divider and render the stop valve conductive.

The control circuit of the firing tube 3| for the first ignitron 5 maybe traced from the control grid Il'Il through the grid resistor I03, anintermediate tap I05 on the resistor 61 in the start valve circuit,conductor 8|, the lower intermediate tap 65 on the divider 55, anotherintermediate tap 85 on the divider, coil 90, and conductor I01 to thecathode 29 of the firing tube. It is then apparent that when the startvalve 51 is non-conductive, the grid ml of the firing tube 3! isnegative with respect to the cathode 29. However, when the start tube 51becomes conductive, the intermediate tap I05 on the resistor 61 inseries therewith and, therefore, the grid IIJI of the firing tube 31,becomes positive with respect to the cathode 29. When the stop valve 84becomes conductive, the cathode 29 of firing tube 3I is connectedtherethrough to the positive terminal 63 of the divider 55 and the gridIIII again is negative with respect to the cathode 29 to prevent thefiring tube 3! from being rendered conductive.

The operation of the relay H is controlled by the oil-time timingsystem, indicated generally at I09. Power is supplied to the off-timetiming system from the supply lines through a switch I I I and anauxiliary transformer I I3. A voltage divider I I5 is connected from oneterminal II1 of the secondary winding II 9 of the auxiliary transformerII3 to the other terminal I2I through an originally closed contact I23of the relay H and an originally closed switch I25. An electricdischarge valve I21 of the arc-like type, preferably a thyratron, hasits anode I29 connected to one terminal II 1 of the secondary winding II9 through a resistor I3! and the energizing coil I33 of the relay H. @Acapacitor I35 is connected in shunt across the energizing coil I33 ofthe relay TI. The cathode I31 of the control valve I21 is connected tothe other terminal IZI of the secondary winding H9 through an originallyopen switch I39, the normally closed contacts I 4| of the relay 92 inthe on-time timing system and the originally closed hand switch I25. Thecontrol grid I43 of the valve I21 is connected to an intermediate pointI45 on the voltage divider II5 through a grid resistor I41 and acapacitor I49; A resistance element I5I is connected in shunt across thecapacitor I49. The originally open contacts I53 of the control relay 1!are connected in shunt across the originally closed hand switch I25.

To operate the control, the hand switch I II between the source and theauxiliary transformer I I 3 is first closed. As a result, the voltagedivider I I 5 is energized, but no current flows through the controlvalve I21 because of the originally open switch I39 in the circuitconnecting the cathode !31 to the secondardy winding II9. Thisoriginally open switch I39 is thereafter closed. As the control grid I43is connected to the intermediate point I45 on the voltage divider I I 5,a gridcathode voltage more positive than the critical value necessary torender the control valve I21 conductive is supplied from the divider iI5 in a half period of the alternating voltage in which the anode I29 ofvalue I21 is positive, such halfperiod, sometimes being referred to as apositive half-period.

6 its contacts l 4 l:aopenitheranodeecathode icircuit -.;--'oi thecontrol valve El 21. 21C onsequently; current flow: 't-hroughirthe:cdntrolwalverkli'l -is;:haited. The control relay II is thendeenergizedssozthat 1 the i stp* va;1ve 843130 'eflect': deenergizatiorrofvthe irelay 92. EUhe contacted I I 0f'this;1e1ayi92: then reclose "theanode-cathode 1 circuit of.'the' .ctmtr01 "-valvesl 27. However,thencontacts 'i 23of the contact tl "thereof completesthe anode circuitof l0rtrol=relay 21f have=also reconnected;the-divider the i start andstop valves and 84 the second contacts '94 "open the discharge l circuitacros s the on time capacitor- 93; -the= third contaots tfi open theCOl'lIlGCtiOr-ibtWQfifl the divider H 5 and the terminal 1 2iof'thesecon'dary *Wiiiding llS;

of the auxiliary transformer -l 13 to which the cathod -l 37* 'of thecontrol valve ['21- is connected; the -fourth contacts l53 close theshunt circuit across theoriginally closed hand switch "I 2 5.

auxiliaryhtransformer 2H3. Consequent1y,x--rthe grid-cathode'woltage 05?I the I control walve' EMT as supplied'i-roml the secondary winding :H 9is; low- .irintermediatecpoint -Il't45 'on' the divider l !5. IIfIhe rcharge :onithei'capacitor M9 is greater v thani this loweredr'grid-hathode' voltage :supplied from the divider H5, and so causes thegrid |43-to- ='be:neg-

when'the-first'c0ntacts'69 ofthecontrol relay ative with respect to thecathode $31.1 Gonsell close, the start valve 51 oftheon-time timingsystem is "rendered'conductive at'the" beginning of the next halfperiocl 'of the altern'atingcurrent-in which the anode' fi'lof firing'tube 31" is *"positive" by "the impulse suppliedthroughthephase-shifting circuit 82. As a result; the firing tube 3| of the 'firstignitron' i-become 'co'nducawe to render that ignitronconductive. Thefollow-up 'system'causes' the second ignitron' l to rquently; theoonta'oi--valve= 1727.- is-hot' rendered 1:\conductive. :ins ai halfperiod iniwhichflts' anode 1 294 is'xpositive-wwhenthe-:anodewathoriemircuit is:'.i'eo1osed aby=- deenergizatiomof therelay 292 -as 2 thew-stop- :valver 844. ceases. to conduct .rcurrent.

- Preferably the moten-tiometer 1'99 risadjusted; so -that the? stop"valve :Mebecomesrconductiven to repent-contacts 44 l; 7 winthet-half-p'e-riodsinw which control valve :12 1- is not conductiveftoavoid arcconduct current during the succeeding 'lialf'pe-e wingatthecontactsv-Ml.

rioclof the alternating-voltage. "The" ignitrons 5 and (thusconduct'current inalternate half-periods' until the stop-valve 84becomes #conductive at a predeterminediater time. -When the stop 'valve84' becomes conductive, the 'grid "1-9 I of the firing tube 31 forthefirst'ignitroh fi b-ecomes'negative' withr-respect to its cathode 29;and, -consequently, the-first ignitron' 5-fai1s' to become "conductiveinthe next' ositive hal'fperiod.

-'-While the on-time't'imingsystem is measuring;

the predetermined' time interval, 'the =capaci-t0rI'MJ'inthe'off-timetiming system is charged. by theygrid' current of thecontrol valve "IZT. "This grid current flows during half periods iof thealternatingivoltage in Whiohthe anode 1 29 of valve T21 is positive, ina circuit from the-terminal "l I! of-thesecondary windingl ls to whichthe anode "T29 is connected; throughthe upper portion of "the divider II5, the capacitor"I 49}- the grid resistor "H1, and the-grid M3 andCathode "I3T 'of the.

control valve $21 to the other'terminal- [2! of ""the'secondary windingH9. Because-of the rectifying-action of the"grid-cathode circuit Withinthe control valve andthe high resistance of the "resistance element 1 5l the-charge on the capacitor flti -may be gradually increasedf lt isto-be notedthat the constants" of the charging i circuit ofthecapa'citor .149 are preferablyarranged so *ith'at the capacitorWillisalmost completely charged in the first or E the first fewp'eriods: of

Y'Phecapacitor W49 sin-1 the off-time: timing-asys- :tem thereafter:discharges through theuhighwresistancee element a l 5 l1 rim: shunttherewith-ata wpredetenmined :rate :depende'nt.=-.upon: the :t-value of'the resistance. After a time interval-dependentmmn -tn e crate ofdischarge of the 1 capacitor,

- :the grid 4431? of the: control -1va1ve= agairrbecomes 1DOSitiVWWith-TTGSPQCE: to its cathode :I-3'l so that the controlvalve=:'-is rendered conductive and a v unewicycleiofroperationisinitiated.

During'i'the Off- .time= interval-while relay H is deenergized, contacts94 of the relay ncomplete u'the discha'rget-circuitzfor the capacit0r 93in the -;:on*time3 timingzsystemrto recondition thatwapac- .1 ito'rrfoirthe next cycle 'ofopcration.

a Thus; currenti willwbe supplied cto thewelding transformer? for:timedwintervals: astldeterin'ined by the ratez of -charge of capacitor:93 irrthe onzx-time timing.- systemy-withwthe timeui'nterval \be- 50-:tween succeSsiVe Qn-time intervals 7: of welding"current"being-determined by thecraterof discharge of capacitor 4:491inithe'z ofifetime timing system. z sW'henit:is'desiredtouhaltxthe:operation :of.- the contro1s -system-;1:theoriginally I closed switch I 25 :inthe 'anode-acathodei circuit qofthe:control valve Mkis opened: and; a11OW8d='f.tO"I8ma1in=T013811, If Fthisrswitch viii-isopened 'during theoff-time: pew-riodr itc-bviouslywpreve'nts the control-valved?! 1e-fronrrbecoming;"conductivetc initiatez sanother on-time period. 21f, the-switchIJ-ZSEismpenedYdur- Wing an onetimeperiod, it 'doesmot render' the 'vcontrol "valve ch21" imm ediately non conductive rbeeause-the contactsi-fiii of: the control-relay H have closed a shuntcircuitabout:the-switch t25. However; as soon: as--the onetime period;is over, i l the control relay- '1 I= is-ydeenergizedwto-open: theshunt: circuit across theswitch I25, and further woperation:ofthesystemis then prevented.

It is tofibe' noted that While; the switches -l 39 1 and/I25 in theanode-cathode circuit of the: control'valverli'l are'shownsashand--switches,-they -may obviously be replaced byrelay contacts orother switch means operatedarfromr a -separate fvtiming circuit-o1icircuits,- if desired. Moreover,

,nrthezrelay fl.inacircuitE'thereWith.istenergizedyand; itiheswitcheslr39:and l=2fi1n ayiunjder somercircumcircuit;

' stances be completely eliminated with the operation of the controlbeing initiated and halted by switches, suchas switch I l l, in thepower supply It is also to be understood that while a discharge pathhaving substantial resistance is to be placed in shunt with thecapacitor I49, it may not always be necessaryto provide a shunt circuitas through resistor ll. For example, the discharge path may -be providedby the leakage resistance path of the capacitor itself if such leakageresistance is of the desired magnitude.

Although we have shown and described a specific embodiment of ourinvention, we are fully aware that many modifications thereof arepossible without departing from the spirit of the invention. It is notour intention, therefore, to restrict our inventionto the specificembodiment disclosed. i

We claim:

1. A timing system comprising a pair of voltage supply lines, anelectric discharge valve of the grid controlled type having an anode anda cathode connected in a circuit across said lines, said valves alsohaving a control grid, a capacitor connected to said grid, a, controlcircuit connected to said capacitor and cathode for impressing a controlvoltage across said connected capacitor and grid and said cathodesuificient to cause said valve to become conductive, a currentresponsivedevice in said anode-cathode circuit operable in response to current ofa predetermined value and associated with said control circuit to makesaid control voltage more positive from said capacitor to cathode, atimer responsive to operation of said device for temporarily preventingcurrent fiow in said anode-cathode circuit a predetermined time intervalafter said device is first operated to cause said device to becomeinoperative, and a discharge path having substantial resistance in shuntwith said capacitor.

2. A timing system comprising a pair or alternating voltage supplylines, a voltage divider connected across said lines, an electricdischarge valve of the grid controlled type having an anode and acathode connected in a circuit supplied from said lines, said valve alsohaving a control grid, a capacitor connected between said grid and anintermediate point on said divider whereby is provided a grid-cathodevoltage to cause the valve to be conductive in positive half-periods ofsaid alternating voltage, first switch apparatus interposed in circuitbetween the divider and one of said lines to which the cathode isconnected and operable in response to current in said anode cathodecircuit in successive positive half periods to disconnect the dividerfrom said one line, whereby a grid current through said valve isproduced to charge said capacitor, second switch apparatus interposed inthe anode-cathode circuit and operable to open that circuit after saidlastnamed means has become operable to prevent said valve from becomingconductive in a positive half-period and then to reclose saidanode-cathode circuit, whereby said divider is reconnected to the lineto which the cathode in connected, the charge on said capacitor uponsaid reconnection being sufiicient to prevent said valve from beingrendered conductive, and a discharge path having a substantialresistance in shunt with said capacitor to effect a discharge thereof ata predetermined rate.

3. A timing system comprising a pair of alternating voltage supplylines, a voltage divider connected across said lines, an electricdischarge valve of the grid controlled type having an anode and acathode connected in a, circuit across said lines, said valve alsohaving a control grid, a capacitor connected between said grid and anintermediate point on said divider, whereby said divider supplies agrid-cathode voltage to cause the valve to be conductive in positivehalf-periods of said alternating voltage, a current-responsive device insaid anode-cathode circuit and operable, so long as said valve isconductive in successive positive half-periods, to disconnect thedivider from the line to which the cathode is connected, whereby a gridcurrent through the valve is produced to charge said capacitor, timingmeans in cluding a switch in the anode-cathode circuit for opening thatcircuit a predetermined time interval after said valve is firstconductive to prevent said valve from becoming conductive and thenreclosing said anode-cathode circuit, whereby said divider isreconnected to said line to which the cathode is connected, the chargeon said capacitor upon said reconnection being sufiicient to preventsaid valve from being rendered conductive, and a discharge path havingsubstantial resistance in shunt with said capacitor to efiect adischarge thereof at a predetermined rate.

4. A timing system comprising a pair of alter nating voltage supplylines, a voltage divider connected across said lines, an electricdischarge valve of the grid controlled type having an anode and acathode connected in a circuit across said lines, said valve also havinga controlgrid, a capacitor connected between said grid and anintermediate point on said divider, whereby said divider supplies agrid-cathode voltage to cause the valve to be conductive in positivehalf-periods of said alternating voltage, a relay device in saidanode-cathode circuit operable, so long as said valve is conductive insuccessive positivehalfperiods, to disconnect the divider from the lineto which the cathode is connected, whereby a grid current through saidvalve is produced to charge said capacitor, timing means including aswitchin the anode-cathode circuit for opening that circuit after apredetermined time interval to prevent said valve from becomingconductive in.

a positive half-period whereby said relay device is deenergized and saiddivider end reconnected to said line to which the cathode is connected,said relay device being efiective when first energized to initiateoperation of said timing means with said timing means effectingreclosure of said anode-cathode circuit after said relay means isdeenergized, the charge on said capacitor upon said reconnection beingsufiicient to prevent said valve from being rendered conductive, andadischarge path having a substantial resistance in shunt with saidcapacitor to efiecta discharge thereof at a predetermined rate.

5. A timing system comprising a pairv of voltage supply lines, anelectric discharge device of the grid-controlled type having an anodeand a cathode connected in a circuit across said lines and also having acontrol grid, a voltage divider connected across said supply lines, acapacitor connected in circuit from said grid to an intermediate pointon said divider, a current responsive device in said anode-cathodecircuit operated in response to current of a predetermined'value todisconnect the divider from the line to which the cathode is connected,a normally closed switch in said anode-cathode circuit, a timeroperatively connected to said switch and operable a predetermined timeafter said device is first operated 10 for temporarily opening theswitch to cause said UNITED STATES PATENTS device to become inoperativeand then reclosing the switch, and a discharge path having sub- NumberName Date stantial resistance in shunt with said capacitor. 1,367,225Lei/an et a1 y 12, 1932 5 2,171,347 Schneider Aug. 29, 1939 WILLIAMLARGE, 2,251,763 Schoene Aug, 5, 1941 U MORTON 2,292,846 Pritchard Aug.11, 1942 2,306,237 Wolfner, 2d Dec. 22, 1942 REFERENCES CITED 2,364,680Wolfner, 2d Dec. 12, 1944 The following references are of record in the10 2366060 Schnelder 1944 fil of t t 2,371,981 w Mar. 20, 1945

